An optical disk recording device (optical disk) using a laser beam has a high recording density and can perform large-capacity recording. Because of an operation in non-contact, the device allows high-speed accessing and its practical application as a large-capacity memory has progressed. The optical disk is classified into a read only type which allows only reproduction, a write-once type which allows only one recording operation at a user side, and a rewritable type which allows repeated recording operations at the user side. The read only type is used for a compact disk or a laser disk, and various types are used for an external memory of a computer and document and image files.
In the read only type, a read signal is detected by using a change in the amount of a reflected light from a concavo-convex pit formed in the optical disk. In the write-once type, a read signal is detected by using a change in the amount of a reflected light from a very small pit formed in the optical disk, or a change in the amount of a reflected light caused by a phase change of a phase change recording film disposed in the optical disk.
In a magneto-optical disk which is one of the rewritable types, recording is performed by irradiating a magneto-optical recording film disposed in the optical disk with a high-output laser beam to change a magnetized state. A read signal is detected by using a magneto-optical effect of the magneto-optical recording film and based on a change in a polarization surface of a reflected light from the magneto-optical recording film. In a phase change optical disk which is another embodiment of a rewritable type, recording is performed by applying a high-output laser beam to cause a phase change in a phase change recording film disposed in the optical disk. As in the case of the phase change optical disk of the recordable type, a read signal is detected based on a change in the amount of a reflected light from the phase change recording film.
Generally, in the optical disk, a thin recording film is formed in a surface of a transparent resin material or glass substrate in which a spiral track groove (pre-groove) is formed at a pitch of 0.615 μm to 1.6 μm. When data is recorded or reproduced, a recording signal of the data is recorded on the recording film or a read signal is detected by tracking of a laser beam spot along the track groove. Generally, only one layer of the recording film is formed in the optical disk.
Incidentally, in the optical disk used for a file device or the like, there is always a demand for achievement of a large capacity, and attempts have been made to meet the demand. For example, in a DVD-RAM, a “land and groove recording system” for increasing a recording density by performing recording in both of concave and convex parts of the track groove has been employed, and put into practical use.
Additionally, there is a “multilayer” method as a method of achieving a larger capacity. This is a method of multiplexing a recording layer in a thickness direction of the optical disk. For example, in a DVD-ROM, an optical disk in which a recording layer is formed into two layers through a spacer layer of a thickness of about 25 to 40 μm has been put into practical use. According to an operation principle of the multilayered optical disk, when recording or reproducing is performed, a focus of a laser beam is offset in a thickness direction to access a desired recording film. In the DVD-ROM, by employing the two-layer formation, a recording capacity is increased from 4.7 GB in the case of one layer of a recording film to 8.5 GB, i.e., larger by about 1.8 times than that in the case of one layer of the recording film.
Studies have been conducted on application of the aforementioned multilayer method to the optical disks of the write-once and rewritable types. For example, in the write-once type, there are proposals of two-layer and even four-layer formations (for example, H. Kitaura et al.; SPIE Proceedings, Vol. 4342, pp 340 to 347, Optical Data Storage 2001.). In the rewritable type using the phase change recording layer, there is a proposal of two-layer formation (for example, K. Nagata et al.; Jpn. J. Appl. Phys., Vol. 38, (1998), pp 1679 to 1686). These proposals also anticipate a capacity increase of about 1.8 from that in the case of one layer of the recording film by the two-layer formation.
However, in the optical disk of the write-once type or the rewritable type using the phase change recording film, the following problem has occurred in the case of multilayer.
In the multilayered optical disk of the write-once type or the rewritable type, a recording layer of a side near a laser beam incident surface must have a fixed transmittance so that a laser beam of predetermined intensity can normally reach a recording layer of a farther side. However, in such an optical disk, because of using of a change in reflectance of the recording film for recording, the recording inevitably causes a change in transmittance of the recording film. Thus, when recording is performed on the recording film of the side near the laser beam incident surface, a change occurs in intensity of a laser beam which reaches the recording film of the farther side, causing a problem of adversely affecting recording and reproducing on and from these recording films. For example, irregular recording or recording loss occurs during recording, or reproduction failures occur during reproducing.
As one method of solving the problem, Japanese Patent No. 2928292 discloses a recording member, among optical information recording members, in which management information for identifying states of a plurality of recording-layers is formed on a recording layer nearest a light source, and a recording and reproducing device. According to this method, however, when recording or reproducing is performed on an information recording medium having a plurality of recording layers, especially when recording or reproducing is performed not on a recording layer of a side nearest a laser beam incident surface but a recording layer of a farther side, unless management information is formed in the layer, a complex process of checking the management information by layer jumping and moving to a desired recording layer by interlayer jumping again is necessary for each recording or reproducing. Thus, there is a drawback that the data recording or reproducing takes long time.
Therefore, objects of the present invention are to provide an optical information recording and reproducing medium, a recording device, a recording and reproducing device, a reproducing device, a recording method, a recording and reproducing method, and a reproducing method, which can perform stable recording or reproducing and a high-speed recording or reproducing operation on the optical information recording and reproducing medium whose recording film is multilayered.